Balancing organization



Aug. 2, 1960 INVENTOR ATTORNEY 2,947,174 Freenet te" 2 itl y A 2,947,174 BALANcnSIr; oRGANl'zA'rIoN Joseph F. Lash, Ferndale, `Mich., assignor to General- Motors Corporation, Detrot, Mich., a corporation of Delaware Continuation of application Ser. No."4"58,172,v Sept. 24,` This application Sept.` V16, '1957, Ser. No;

.'10 Claims. (Cnn-:464i

" tional balancing practice, the crankshaft is coupled'to the gated rotating workpieces such as'cranks'hafts and the like. TheV invention is specially 4suited for nse in engine l assemblyor finish balancing installations in which the crankshaft is checked for unbal-ancewheninstalled vin an engine and any unbalance in the shaftuand ,such unbalance asrmay be contributed 4thereto bythev other components of the enginel associated withrtheshaft' corrected inv the assembled condition of the engine. Y

\ The invention has lamong its general objects-"to provide such ,apparatusin accordance with theabovefand which is characterized by extreme simplicity `of construcshaft 18 of the drive motor through fa suitable coupling arrangement shown at SIL-which may comprise a pair of `spaced universal joints that permit free oscillation of the shaft under the influence of unbalance Vforces therein.

The vibration pickups Z2 and 24 are mounted transversely` to the axis of the shaft and at spacedpoints along the length of the cradle corresponding to the mechanical nodal points of the unbalance forcesat the respective ends of thecrankshaft in accordance with the theory `and practiceI setout in United States Patent 2,293,371 in the name of T. v`C.`Van Degrift assigned to -the present assignee. The pickups 4are conventional electro-magnetic devices each of which generates an alternating current signal proportional to the velocity of the oscillatory vibrations appearing at the respective onesof the laforementioned nodal points, and, by reason of the nodal point mounting thereof, are i' unaffected by the unbalance iniiuence of the opposite end-ofthe shaft. `The alternating current signal from each of the pickup devices has a frequency equal to the rotational speed at which the'crankshaft is driven and an amplitude proportional to the total unbalance effect produced vby theend ofthe shaft adjacent the pickup. Each pickup signal further includes aphase displacement characteristic that is related to the angular location of thetotal unbalance from `a iiXed point, which tion and offopera'ti'on and, iy'et, Ypossessed of sufficient sensitivityiand a 1 high'degr'ee of 4'ac'ciira'cy'x-and i'which Vis adapted to lbe "intimatelyl associatedwith unbalance l correctinglapparatus that is automatically*adjusted during thefdeterminationoffthe 'characte'risticii-1'of iibala Y electingj 'balancef correctibnsf to sucht devices minimum of'human' interventi The above and other objects, togetheriwiththe featnij'esandffadvantages attending the, present-invention -will appearjmore fullyfom the following detailedldescrilition and schematic and block diagrammatic" showing of a balancing apparatusginaccordancefwithithe present invention. 1 .v

*y "In the drawing, 10 is anY engine assembly-'having a 4crankshaft;shown "at 12I therein and mountedwith the oil pan cover removedfin an oscillatabley engine stand oi cradle 14.l jThe workpiecemay be driven byv an "electric drive motor 16 which is provided -for 'rotating'theworkf piece *during/the unbalancedetermina'tion operation." This motor 16v is preferablyjf constant speed; The shaft r1S of the'motor 16 has an angularly graduated hand'wheel "i 20 4mounted thereon and is suitably coupled to 'theengine crankshaft 12 to rotate the latter on its aXisfin the cradle or stand. Vibration pickups 22 and24 are provided at each end of the workpiece to be responsivet'o the'vibrations createdby any unbalance therein-and Agenerate siggnals indicative of the unbalance. "Each'of -the pickups is associated with yan unbalance magnitude and location determining apparatusand an element"ofan unbalance magnitude correcting devicein `"accordance with Vthepres'- ent invention, Only the set of the unbalance determin'- ing apparatus and the eleme'ntvof` an unbalancebrnagnitude cnfrecting' device'forpickup, 22I is shown' in "the draw-- ing., This is for the most part of la diagrammatic nature to bring outV principles of operation rather than particular details of construction.V I l Y .y y The. engine Stand crfcradleflt `isofff'i, iYP'ef'emPlyd in conventional vbalancing install itions'` is onjthe'surface ofthe shaft,- and may be contained in a transaxial correction plane extending through an 'end counterweight ofthe shaft, there being two such cor= rectionnplanes =for theishaft.

"i" Pickup Zftogether with the apparatus associated therewith, isfadapted, therefore, Y'to -sensetheY characteristics 'of nbalance Aat the left `end of the shaft and has its outputi'ainpliiiedin an amplifier 34,- the outprut of which is Relay coil 56 isl connected for energization in a circuit' whichy is periodically actuated in response to the rotation 1 of the workpiece. The actuation of the relay is preferably by means of a square wave of 180 duration and having a known phase relation to the workpiece. A1- though there are numerous generators64 for creating such a wave, in the present instance it is accomplished by a mechanical make and break Vswitch S-1 actuated Vbya cam 66 rotating with the drive motor shaft. The square wave generator 64 also includes Va second S-Z which is actuated by a second cam 68 similar to the first but Voriented therefrom. Each cam has associated therewith a pair of circuit contacts 70, 72, and 74, 76, which are stationary and are alternately closed and opened for each revolution of the shaft 69. This will generate a pair of square waves, 90 out of phase with each other. Suitable ganged means 78- associated with the cams and including acontrol knob 80 is provided for angularly displacing thecams relative to their contacts to lalt'er'thel commencement of the half period'during which the colitacts 70, 72 and 74, 76 are closedand opened relative to a xed reference point'onfthe crankshaft.

Thefenergizing circuit-for `relay coil Y56` includes conductor '82, asource of fpowersuch as battery 84,condu'c" tor-86, contacts 70,72 and? conductor 88. The-movable switch arm 54 of the relay 48 thus is alternately moved between 'itsf contacts '50, 5 2 to 2 provide va `reversing` or commutatingl actionof the ampli-tied: pi'ckup` sign-alf.V

device 40 betweenv conductors 90 and lStZ, which are con nected to switch a-rm 54 and the center tap of the transformer secondaryy winding, respectively, and may be dis. played on a zero center. D'.,C. mill-iammeter 9"4 Connected betweenconductors 90 and 92. Rotation ofthe control knob 80 by the operator to adjust the positionof the cams 66 and 68 with respect to the crankshaft will vcause the amplitude of the full -wave rectified signal displayed on. meter 94 to vary from zero to maximum.- Thecontrol knob y80 is provided with angular graduations thereon so that its angular displacement relative to a reference pointer 96 on a stationary panel or the frame 98 of the contact mechanism 64 may be read for a zero or null reading of meter 94 .as an indicationof the angular location of the unbalance in, sayythe left end of the crankshaft. f

. y Y 4 matically in accordance with the determination of unbalance.

The two cams 66 and 68 of the contact mechanism 64 both move as the operator adjusts the control knob 80 for zero or null reading on the D.C. meter 94. The output of chopper 40, which is associated w-ith the unbalance location orangle determining portion of the apparatus, is then zero while that of chopper 100, which is associated with the quadrature lrelated cam 68 of the unbalance magnitude determining portion of the apparatus, will be a maximum. After the angular location of the unbalance has been readby the operator from the control knob 80 andthe drill depth stop element 134 has been automati- The amplitude or magnitude ofthe total unbalance at l l the left end of the shaft is determined by applying the amplified pickup signal appearing at the output of amplifier 34 to a second 'chopper device 100 which may be similar to chopper Y40. This chopper 100 also includes `a transformer 102 having `a primary winding 104 and a center tapped Ysecondary winding 106 and a relay contactor 16S with a switch arm 110 movable between a pair of stationary contacts 112 and .1i14 by an energizable -actuating coil 116. Actuating coil 116 is connected in an energizable circuit which -includes conductor 118, battery 120, conductor 122, contactor 74 and 76 of contact mechanism 64 and conductor 124. A

rllhe commutated output of the second chopper 100is taken from the center tapped secondary winding :106 and switch arm 110 and applied as a full wave rectified signal over conductors 130, 132 to a closed loopservo controlled amplitude comparison circuit which automatically indicatesthe magnitude ofthe unbalance quantity and positions an adjustable dr-ill stop setting element ,134 ofa balance correction drilling organization associated with the unbalance determining apparatus to effectexactcompensation for the amount of the unbalance at the left end of the shaft. The/amplitude comparison and drillstop positioning apparatus includes a conventional servo amplier 136 and its associated twophase servo motor 1 38 and a potentiometer arrangement comprising the adjustable resistor 140 connected across a xed, known reference source of balance voltage, shown as battery 142. The output of the second chopper100 is connected in series with the input of the servo amplifier and the portionl of the output of the potentiometer appearing between conductor 132 and the adjustable arm 144 of the potentiometer resistor 140, which is mechanically coupled to the shaft 146 `of the servo moto'r 138.

One of the phase windings of the servo motor 138 is connected for energization from a local alternating current source of supply and the other quadrature phase winding thereof connected for energization by a control signal which appears at the output of the servo amplier and corresponds to the amplitude difference between the output of the chopper and-the potentiometer. The resulting differential control signal is of such magnitude and polarity as to tend to rotate the servo motor in a direction and an amount such as to reduce the error or control signal to zero at which point the comparison system wiil be balanced and the motor or translating device will cease moving.

An indicating arrangement in the form of a graduated indicator dial 150, which may be provided on, say, the stator casing of the servo motor 138, and a pointer 152 carried by the shaft 146 may be employed to indicate the magnitude of the unbalance. In accordance with the invention the shaft 146 of the servo motor 138 is directly coupled to the drill depth control element 134 of a balance correcting drilling organization or equivalent balance correcting apparatus, which is mounted under the engine assembly, and adjusts. the drill depth setting element autocally adjusted by the servo motor of the self-balancing amplitude comparison circuit, the drive motor is stopped, the operator manually adjusts the hand wheel 20 to position the exposed counterweight of the crankshaft where one of the balance corrections is to be performed over thevdril-l bit of the drilling organization mounted below the engine stand and thereafter energizes the drill motor and transmission apparatus thereof to remove an amount of metal corresponding to the setting of the auto. matically adjusted drill depth setting element from the counterweight in the left end correction plane. The operation is repeated for the right end of the shaft.

The use of the chopper integrating apparatus for'the unbalance magnitude determining portion of the unbal# ance computing apparatus assures that the unbalance signal obtained from the output of the chopper will be unafected by and will be independent of all frequencies other than the fundamental frequency determined by the speed of spindle 69. In short, the chopper acts as a very narrow band pass filter.

.Y Pickup 24 is adaptedA to sense unbalance effects in the right end of the crankshaft and will have its output applied'to anr unbalancerldetermining and drill depth control apparatus A.including aA second contact mechanism and a. second setof vangle location and unbalance magnitude choppersand associatedV apparatus identical with that associated with pickup 22, ythe complete4 illustration of which has been omittedV for simplicity of the drawing. l

What is claimed is; ,4 :'11, Apparatus for determining the magnitude and angular location of unbalance of a dynamically unbalanced body comprising in combination, means supporting the body for rotation about its axis; drive means rotating the body on its axis; vibration pickup means responsive to vibrations induced by unbalance in said body and developing 'a periodically varying signal having characteristics related to the magnitude and the location of unbalance in said body; a pair of commutating chopper devices each having a transformer with a primary winding connected to said vibration pickup means and a center-tapped secondary winding, a relay having a pair of stationary contacts connected to the opposite ends of said secondary Winding and an armature movable between said cdntacts by an operating coil of the relay, a variable contact mechanism including a pair of cams displaced degrees apart and driven by said drive means in synchronism with said body, a pair of switches each having a pair of switch contacts and adapted to be actuated by a different vone of said cams, and adjustable means for changing the position in space of said switches relative to said cams, the said switch contacts of each of said cam operated switches being connected in separate energizing circuits for the relay operating coil of a different one of said chopper devices; a null indicating device connected to the output of one of said chopper devices constituted by the relay armature and center tap of the transformer secondary winding associated with said one chopper device; and a self-balancing type of amplitude comparison circuit connected to the output of the other of said rchopper devices.

2.v The combination in accordance. with claim 1 wherein said self-balancing type amplitude comparison circuit includes fanadjustable' known source ofbalancing potentialanda servo motorj'whichis actuated by the dilerence signal between thev commtated 'outputof `one of said chopper devices and said adjustable known source of balancing potential and is operatively connected to adjust the ,latter to.` reduce the saidl diierence signal to zero.

3. The combination inv accordance with claim 2 which in cludes`an adjustable stop element positioned by said servo motor in accordance with the magnitude of unbalance in said body determined inthe course of balancing saidself-balancing amplitudel comparison circuit.

4.` In apparatus for determining the magnitude o'f vunbalance of a dynamically unbalanced body including means supporting the body for rotation about its axis, drive means coupled to said body for rotating the latter on its axis, and vibration pickup means responsive to vibratio'ns induced by unbalance in said body and developing a periodically varying signal having characteristics related to the magnitude of unbalance in said body; the combination of unbalance magnitude determining means including'a commutating chopper device having a transformed with a primary winding connected to said vibration pickup means and a center-tapped secondary winding, a relay having a pair of stationary contacts connected to the opposite ends of said secondary winding and an armature movable between said contacts by an operating coil of the relay, a variable contact mechanism including a cam driven .by said drive means in synchronism with said body and a pair of switch contacts adapted to be actuated by said cam, and adjustable means for changing position in yspace of said switch contacts relative to said cam, said switch contacts being connected in an energizing circuit for said relay operating coil; and

utilizing means connected` to the output of said chopperA device constituted by the relay armature and center tap of the transformer secondary winding and indicating the magnitude of unbalance in said body.

5. Apparatus for determining the location of unbalance of a dynamically unbalanced body comprising in combinatlon, means supporting the body for rotation about its axis; drive means including a rotatable shaft coupled to said body fo'r rotating the latter on its axis; vibration pickup means responsive to vibrations induced by uubalance in said body and developing a periodically varying signal having characteristics related to the location of unbalance in said body; unbalance angle `determining means including a commutating chopper device having a transformer with` a primary Winding connected to said vibration pickup means and a center-tapped secondary winding, a relay having a pair of stationary contacts connected to the opposite ends of said secondary winding and an armature movable between said contacts by an operating coil of the relay, a variable contact mechanism including a cam driven by said drive means in synchronism with said body, a pair of switch contacts adapted to be actuated by said cam, and adjustable means for changing position in space of said switch contacts relative to said cam, said switch contacts being connected in an energizing circuit for said relay operating coil; and a null indicating device connected to the output of saidchopper device constituted by the relay armature and center-tap o'f the transformer secondary winding.

6. In apparatus for determining the magnitude of unbalance of a dynamically unbalanced body including means supporting the body for rotation about its axis, drive means coupled to said body for rotating the latter on its axis, and vibration pickup means responsive to' vibrations induced by unbalance in said body and developing a periodically varying signal having characteristics related to the magnitude of unbalance in said body; the combination of unbalance magnitude determining means including a commutatingchopper device having a transformer with a primary winding connected to said vibration pickup'means and a center-tapped secondary windirfgg? a` relay 'havi1`1'gV Va pair of stationary" contacts connected Atoith'-cip'pbsite ends of said' secondary winding and Van""armature movable" lbetween said. contactsV byan operating'coil rof the/relay, a-variable contact mechanism including acanidriven'byi said drive means in synchronism'wi'th said `body and a pair of switch co'ntacts adapted to be'vv actuated byf-said Vcarrnand"adjustable means for changing ffpositin-- 'in lspacemf said switch contactsrelativ`e to said cam, said switch contacts being connected in an energizing circuit for said relay operating coil; and a self-balancing type' amplitude comparison circuit connected to the outputoflsaid chopper device.

f "7. tThef combination in accordance with claim 6 wherein said self-balancing type amplitude comparison circuit includes an adjustable known source of balancing potential and a servo motor, which is actuated by a signal proportional to the difference signal between the commutated o'utput of said chopper device and said adjustable known source of balancing potential and is operatively connected to adjust the latter to reduce the said difterence signal to zero.

8. The combination in accordance with claim 7 which includes an adjustable stop element of an unbalance correction apparatus positioned by said servo motor in accordance with the magnitude of unbalance determined in the course of balancing said self-balancing amplitude comparison circuit and transmission means between said servo motor and said adjustable stop element for positioning the latter to co'ntrol the extent of unbalance correction to be performed on said body subsequent to the unbalance determination thereof.

9. In apparatus for checking the existence of dynamic unbalance in the crankshaft and the components associated therewith of an assembled engine and determining the magnitude of any dynamic unbalance therein, the combination of a vibratile cradle mounting the assembled engine therein; a motor coupled to the crankshaft and rotating the crankshaft about its axis in said engine; a vibration pickup responsive to the vibrations of said cradle induced by unbalance of said crankshaft and associated engine components and mounted at a vibration nodal point of said cradle, said pickup developing a periodically varying electrical signal related to the magnitude of dynamic unbalance in said engine; unbalance magnitude determining means including ia commutating chopper device having a transformer with a primary winding connected to said Vibration pickup means and a center-tapped secondary winding; a relay having a pair of stationary contacts connected to the opposite ends of said secondary winding and an armature movable between said contacts by ran operating coil of the relay, a variable contact mechanism including a cam driven by said drive means in synchronism with said body and a pair of switch contacts adapted to be actuated by said cam, and adjustable means for changing position in space of lsaid switch contacts relative to said cam, s aid switch contacts being connected in an energizing circuit for said relay operating coil; and utilizing means connected to the output of said chopper device constituted by the relay armature and center tap of the transformer secondary winding and indicating the magnitude of unbalance in said body.

l0. Unbalance measuring apparatus for measuring the unbalance in a rotating workpiece comprising, circuit means having a pair of separate portions, each of said portions having a rst inductive input and a second inductive input, at least one of said inputs in each of said portions comprising the primary of a transformer, a vibration pickup for creating an unbalance signal indicative of the unbalance in said workpiece and interconnected with the pair of said Aiirst inputs, each of said portions having a secondary winding inductively coupled to said primary windings, said secondary windings each having -a center tap and a pair of end taps, each of said portions having commutating means for alternatively connecting said end taps to a arst lead, said center Vtapageaelycon-i nected to a second lead, said first of second leadsof each portion forming an output for jeach oljsaidy portions, reference means actuated in response to the rotation of said workpiece to generate a pair of electrical reference signals ninety degrees out of phase with each otherv and having a known phase relation relative to the angular position of said workpiece, said reference means being interconnected with said commutating means for energizing said commutating means to cause the same to demodulate the unbalance signal from said inputs and produce a pair of `output signals in said outputs, means for adjusting said reference means to vary the phase relation of said reference signals Irelative-to said workpiece sothat the signal in said second pair of inputs can be varied until one of said output signals is a minimum and means for observing the other of said output signals.

References Cited in the file of this patent UNITED STATES PATENTS 10 2,243,379 Johnson V May 27, 11941 2,451,863 Oakley Oct. 19, 1948 2,636,381 Hagg et al Apr. 28, 1948 2,731,835 Hellar et al. Jan. 24, 1956 

